Electron discharge apparatus utilizing a cavity resonator



ELECTRON DISCHARGE APPARATUS UTILIZING A CAVITY RESONATOR Filed NOV. 30, 1951 INVENTOR ERNEST [5. LINDER Patented Jan. 26, 1954 2,567,593 ICE ELECTRON DISQHAR GE APPARATUS UTILIZ- ING A CAVITY RESONATOR Ernest G. Linder, Princeton,

N. J., assignor -to Radio Corporation of America, a corporation or Delaware Application November 30, 1951, Serial No. 253,112

9 Glaims.

The present invention relates to improvements in electron discharge apparatus, and particularly, to novel output terminals for high frequency electron tubes of the beam type utilizing cavity resonators, such as velocity modulation tubes, for example.

In conventional electron tubes of the kind mentioned, an electron beam is passed through one or more cavity resonators toward va collector or reflector electrode positioned beyond the last resonator, and the output is taken from said last resonator by means ofacoaxial line or waveguide coupled to the electro-magnetic field within the resonator independently of the collector or reflector electrode and its direct currentlead.

The object of the invention is to provide an improved output structure for beam tubes of the cavity resonator type.

In accordance with the invention, the output of such a tube is taken from a section of coaxial line which either constitutes or forms part of a coaxial tube terminal of which the collector or reflector electrode lead is also a part. This output coaxial section is made up of an outer tubular conductor which surrounds the collector or reflector electrode and its lead and an inner conductor which may be either said electrode and lead, in one embodiment of the invention,or a second tubular conductor telescoped between the outer tubular conductor and said electrode and lead, in another embodiment. The output coaxial section is electromagnetically coupled at one end to the output resonator of the tube by one or more apertures, and is sealed at its other endatsaid output terminal. The output coaxial section may be coupled at said terminal directly to a coaxial load line. Alternatively, the output coaxial-sec tion of the tube may be coupled at said terminal to a tunable device, such as an external coaxial line section of adjustable length, to vary the .resonant frequencyof the system.

In the annexed drawing:

Fig. 1 is a longitudinal sectional view of an electron beam tube embodying the present intion;

Fig. 2 is a transverse line 2-2 of Fig. 1;

Fig. 3 is a view similar to Fig. 1 of a similar tube incorporating the invention;

Fig. 4 is a transverse sectional view taken on line 5-4 of Fig. 3;

Fig. 5 is a view similar to fication thereof; and

Fig. 6 is a transverse line 66 of Fig. 5.

The three electron tubes shown in Figs. :1, '3 and 5 are velocity modulation tubes of thereflex type, sometimes. called Reflex Klystrons,-.where.- in an electron beam from an electron gun-passes through -an.=aperture .in .a .single cavity resonator and is then reflected by a negative reflector electrode back through the resonator.

sectional view taken on Fig. 1 showing a modisectional view taken on provided between trode are brought Referring to Figs. 1 and 2, the tube envelope comprises a tubular metal member I and a cupshaped glass closure member 3 sealed thereto. The electron gun comprises a cathode -5, heater 1 and focusing ring 9 coaxially mounted by suitable means (not shown) within the member 'I. A reflector electrode -I i is mounted on the axis of the gun by means of a lead 53 extending coaxially through a glass member I which hermetically seals a reduced-diameter end part -I 'l of the member I.

Two spaced grids '1 9 and 2|, positioned between the cathode 5 and reflector I I, are mounted across apertures of two annular metal members 23 and 25 which cooperate with the connecting part of member to form a toroidal cavity QS- onator 21. The annular member 23 is solid, except for its central aperture, and is supported within the member I by a peripheral flange 29. The annular member 25 is smaller in diameter than the member I and is ally-extending narrow legs 3|, preferably integral with the member 2 5, engaging the inner surface of member I. An accelerating grid 33 may be leads for the cathodeQheater and focusing elecmember 3, as shown in Fig. l. a

The reflector II and lead I3 and thesurroungzling part of the metal envelope member! form the inner and outer conductors ofan output coaxial line output section 35. This section is coupled tothe resonator 27 through four coupling apertures 37 formed by the openings defined by the members I and 25 and the four legs 3|. The outer end of the section provides an external coaxial terminal 39 for the tube, to which a coaxial load line may be coupled.

The coaxial section 35, and

axial tuning stub 4| coupled to the terminal 139. The stub 4| comprises outer and inner conductors 43 and 45 coupled at one end topart I7 and lead I3, respectively, and a slidable piston 41. The output may be taken from the stub 4| by means of a coaxial line 49.

In the operation of the tube, electrons from cathode 5 are accelerated by grid 33 toward the two grids =I9 and 23 ofresonator '27 atsubstantially uniform velocity. As they cross the resonator; gap formed by thetworesonator grids they are velocity-modulatedi. e., either accelerated or decelerated depending upon the instantaneous phase :01 the electric field in the resonatoiflgap, during their passage therethrough. As the emctrons subsequently travel toward the reflector and then back to the resonator, they become bunched'axially of the beampath, as a result of their differences in velocity. When the electrode spacings are suitably chosen the electronbunches pass through the resonator 27 proper phase to drive the resonator at its resonant frequency,

supported by four radi- 1 the gun and grid I9. Biasing out through the glass envelope hence, the cavity resonator 21, may be tuned by means of a co-,

' fThe tube shown in 3 that is, to induce an electromagnetic field of that frequency within the resonator.

In Fig. l, the reflector H is located within the electromagnetic field of the section 35. The coupling between the resonator 21 and the section 35 is such that the field between grid 2| and reflector II is much weaker modulating field between grids l3 and 2|, and hence, does not appreciably affect the bunching process. If the tube is to be used without the tuning stub, feeding directly into a load line, the coupling apertures 31 should be made much smaller and reduced in number, as in Figs. 3-6, to avoid excessive loadingof the resonator 21.

Figs. 3 and 4 is similar to that of Figs. 1 and 2 except for the output structure. The resonator member 25 is replaced by a ring which is solid except for the central aperture for the grid 2| and a single, relatively-small, coupling aperture 53. A tubular ccnductor 55 is interposed between the reflector H and its lead It and the outer member I, with one end connected to the ring 5! around the grid 2i and inwardly of aperture 53, as shown. The conductor 55 and surrounding member 1 form an output coaxial line section 51. The outer ends of the members i and 55 and the lead K5 are sealed by glass rings 59 and El and form a three-element coaxial terminal 53 for the tube.

The operaticn of the tube of Figs. 3 and 4 is similar to that of Figs. 1 and 2, except for the omission of the tuning means. The reflector H andlead l3 are shielded from the electromagnetic field by thetubular conductor 55 and grid 2i.

Figs. 5 and 6 illustrate amodification of the tube of Figs. 1 and 2 incorporating a capacitive by-pass between the reflector and the adjacent resonator wall. The resonator wall 65 is provided with a re-entrant part 51 which is capacitively couplecl to a flange 69 provided on the periphery of the reflector 1|. The resonator wall 65 is formed with a single coupling apertur 53, asin Figs. 3 and 4. The reflector lead is a conical element '53 which cooperates with a conical part of the member I to provide a tapered coaxial line transition section Tl between the resonator 2'! and the output terminal 39. The efiect of the by-pass B'i-B9 is, of course, to shield the gridrefiector region from the electromagnetic field of the resonator 27 and the output coaxial section H.

It will be understood that, if desired, the coupling may be increased and a tuning means may be coupled to the terminal 39 in Figs. 3-6, as in Figs. 1 and 2.

What is claimed is:

1. Electron discharge apparatus comprising a cathode and an electrode defining'a beam path therebetween, an output cavity resonator having a gap surrounding an intemediate portion of said beam path, and an elongated tubular conductor surrounding said electrode and connected at one end to an outer part of said resonator, said resonator being formed with at least one aperture outwardly of said gap and opening intothe space within said conductor and providing restricted electromagnetic coupling between said resonator and said space, said tubular conductor constitut ing the outer conductor of a coaxial line output terminal for said apparatus.

2. Electron discharge apparatus according to claim 1, further including an elongated conductor extending from said electrode and constituting the inner conductor of said terminal.

3. Electron discharge apparatus according to claim 1, further including a second tubular conductor surrounding said electrode and connected at one end to said resonator around said central than the principal velocity I gap and inwardly of said aperture, said second tubular conductor constituting the inner conductor of said terminal.

4. Electron discharge apparatus according to claim 1, further including tunable means coupled to said terminal. for varying the resonant frequency of said apparatus.

5. Electron discharge apparatus according to claim 1 further including means hermetically sealing the other end of said tubular conductor, said means and said tubular conductor forming a part of a vacuum envelope for said apparatus.

6. Electron discharge apparatus comprising a cathode and an electrode defining a beam path therebetween, having a central gap surrounding an intermediate portion of said beam path, and an elongated" tubular conductor surrounding said electrode and connected at one end to an outer part of said resonator, said resonator being formed with at least one aperture outwardly of said central gap and opening into the space within said conductor and providing restricted electromagnetic coupling,

between said resonator and said space, said tu-.

bular conductor constituting the outer conductor of a coaxial line output terminal for said apparatus.

7. Velocity modulation grids and a reflector electrode spaced along a beam path in the order named, a toroidal output surrounding and coupled to saidv netic coupling between said resonator and said terminal.

8. Apparatus according to claim '7, wherein said reflector electrode is positioned within the elec'- tromag'netic field of said terminal and serves as an output coupling element.

9. Velocity modulation electron discharge apparatus comprising a cathode, first and second grids and a reflector electrode spaced along a. beam path in the order named, a toroidal output cavity resonator surrounding and coupled to said grids, and a coaxial line output terminal for said apparatus including two concentric elongated tubular conductors surrounding said reflector electrode and connected at one end to said resonator around said second grid, said resonator being.

formed with at least one aperture opening into the space between said tubular conductors and.

providing restricted electromagnetic coupling between said resonator and said terminal.

ERNEST G. LINDER...

References Cited in the file of this patent UNITED STATES PATENTS Number Name. Date 2,409,640 Moles Oct. 22, 1946' 2,410,822 Kenyon Nov. 12, 1946 2,464,801 Gardner Mar. 22, 1949 a toroidal output cavity resonator electron discharge apparatus comprising a cathode, first and second Litton May a, 1951: 

